Developmental support in early parent-infant interactions has been shown to predict children's early development and later academic success, but the long-term combined impacts of maternal and paternal interactions are rarely examined. For 229 low-income children in the US Early Head Start Research and Evaluation Project, parent-toddler interactions at age 2, observed separately with fathers and mothers, were examined in relation to child outcomes at age 3 and 5th grade. In families with resident biological fathers, both mother and father cognitive stimulation independently predicted 5th grade math and reading, over and above program impacts and child gender. In other families, only mother cognitive stimulation predicted later child outcomes, even if fathers were involved in children's lives. Adding early developmental indicators to the model showed that the contributions of mothers' early cognitive stimulation on children's later academic skills were significantly mediated by children's early development in biological father-resident families, but not in other families. Similarly, adding early developmental indicators to the reading model showed that the contributions of fathers' early cognitive stimulation on children's later reading was partially mediated by children's early vocabulary in biological father-resident families, but not in other families. These results suggest that fathers' and mothers' cognitive stimulation in early play with toddlers both have the potential to make long-term direct and indirect impacts on their children's academic success.